1. Field of the Invention
This invention relates to devices used to monitor the brake wear and adjustment on vehicles employing air brake systems, such as, trucks, tractor trailers, buses and the like. The new device provides a simple means to install a monitoring system for monitoring each of the brakes of a vehicle.
2. Description of Related Art
There are currently published and known systems in the art which typically use a permanent magnet as a basis for measuring brake wear wherein the magnet is mounted to a rod which moves when the air brakes are activated. For example, the push rod of a brake system travels a certain distance when air pressure is applied to an air chamber assembly which distance is a function of brake wear and adjustment of the brake assembly. A magnetically activated switch is used in cooperation with the magnet such that if the push rod moves a certain distance the switch is activated to signal that the brake must be attended to for repair. Examples of such systems are disclosed in U.S. Pat. No. 4,757,300 and 4,855,712.
Other attempts to use measured motion of the push rod, other brake rods and rotation of the connection between the push rod and shock adjuster arm have also been proposed. In U.S. Pat. No. 5,689,231, a transducer engaged with a clevis pin monitors rotation relative to the push rod and shock adjuster arm to provide indication when brake repair may be necessary.
The present invention provides a simple mechanism for monitoring brake wear and adjustment by using a cable attached to a pull or breakaway switch to signal when the air brake system push rod has traveled beyond a predetermined distance relative to the air chamber. This device is relatively easy to install on existing brakes using for attachment points existing threaded bolts, screws and the like. The pull or breakaway switch may be a rugged self contained unit with two electrical leads and have a simple cable attachment. No devices need to be mounted to the push rod obviating the concern for proper location of such units.